Double-acting hydraulic dirt ejector



Sept. 23, 1958 T. o. DAVIDSON ETAL 2,353,201

- DOUBLE-ACTING HYDRAULIC DIRT EJECTOR Filed Oct. 15, 1953 3 Sheets-Sheet 1 INVENTORm TRE OR DAVDSON IJAmEs E. ROCHE,

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Sept. 23, 1958 T. o. DAVIDSON ETAL 2,853,201

DOUBLE-ACTING HYDRAULIC DIRT EJEICTOR Filed Oct. 15, 1953 3 Sheets-Sheet 25 L m 6C 56 f 58 i1 i 34 mod 62 55 7 5 o 4 3 5! a 4-41: m D 6] 56 E :iz::::::.2

57 I o 58 59 E E v j A75 1 A 50 I TREVOR. DAVlD sow, JAMES E. ROCHE) IN VEN TORS AT ORNE nited States DOUBLE-ACTING HYDRAULIC nin'r ninc'ron Trevor 0. Davidson and James E. Roche, Milwaukee,

Wis, a'ssignors to Bucyrus-Erie Company, South Milwaukee, Wis., a corporation of Delaware Application October 15, 1953, Serial No. 336,195

8 Claims. (Cl. 214-510) This invention relates to new and useful improvements in backhoe-type excavators and more particularly to an hydraulic dirt ejector to be used on the dipper thereof.

Hydraulic backhoe-type excavators are generally used for ditching and trenching operations. They are desirable for digging narrow, shallow trenches, but the machine constructed in such a manner so as to be pivoted at the open upper end of the dipper so that, when moved, it will sweep through the dipper cavity to eject the dirt therefrom. Heretofore, this ejector has been poweractuated in its positive motion for dumping and cleaning out the dipper, and then returned to its normal digging position by a spring. This spring-return has proved insuliicient, in that dirt, stones, and debris have backed up behind the ejector plate, resulting in jamming the ejector in the dumping position preventing its return to the retracted or digging position. Thus, digging must be interrupted by stopping the machine and manually cleaning the bucket.

It is the general object of this invention to provide an efiicient hydraulic ejector for a power-backhoe that will return itself automatically by power means to the digging position after dumping the dipper but before the dipper is to be reloaded. It will be seen that this is achieved in this invention by a double-acting hydraulic cylinderpiston assembly interconnected into the hydraulic circuit of the digging ram hydraulic cylinder piston assembly so that the resistance differential between these assemblies will normally allow return of the ejector to the retracted position before digging another dipper full of material.

A further object of this invention is to utilize the hydraulic pressure of the main hydraulic system of the excavator to return the ejector to the retracted position, but to utilize an auxiliary hydraulic source to supply power to operate the ejector in its positive or dumping movement so that the ejector may be selectively used or not used whichever the need may be.

A still further object is to interconnect the retract end of the double-acting hydraulic cylinder-piston assembly connected to the ejector with the hydraulic cylinderpiston assembly furnishing the digging force so as to reduce the number of conduits necessary and eliminate unnecessary wear and duplication of parts.

A still further object is to eliminate the loaded spring ejector return and thus reduce the size of the hydraulic cylinder-piston assembly used on the ejector. This is made possible by the fact that this cylinder-piston assematent Patented Sept. 23, 1958 ice bly does not have to overcome the force of a spring while ejecting the dirt from the dipper.

In addition to the objects stated above, a number of novel and useful details have been worked out, which will be evident as the description progresses.

This invention consists in the novel parts, and in the combination and arrangement thereof, which are defined in the appendant claims, and of which two forms are exemplified in the accompanying drawings, which are hereinafter particularly described and explained.

Throughout the description, the same reference number is applied to the same improvement or to similar improvements.

Figure 1 is a side elevation of an hydraulic backhoetype excavator, showing the digging ram located on the top of the boom.

Figure 2 is a side elevation of the same type excavator, except that the digging ram is shown as located on the bottom of the boom and further, that the dipper sheave is fastened directly to the dipper handle.

Figure 3 is an enlarged side elevation of the dipper of Figures 1 and 2, showing the ejector and double-acting hydraulic ejector ram.

Figure 4 is a rear elevation of the dipper and ejector shown in Figure 3.

Figure 5 is a schematic diagram of the hydraulic system showing the interconnection of the hydraulic conduits of the digging ram and the double-acting ejector ram for the first embodiment of this invention corresponding to Figure 1.

Figure 6 is a schematic diagram of the hydraulic system showing the interconnection of the hydraulic conduits of the digging ram and the double-acting ejector ram for the second embodiment of this invention corresponding to Figure 2.

Referring now to the figures, and more particularly to Figures 1 and 2, we find that 11 is the main frame of the excavator (shown in outline only), 12 is the nearer one of the two rear wheels of a conventional mounting for this type excavator, and 13 is the nearer of the two out-rigger ground-supports which act to stabilize the excavator mounting while the excavator is in use. The upper works is connected to the lower works by a pintle 14 so that the upper works may rotate with respect to the lower works. An A-frame 16 comprises a part of the upper works, and the boom 17 is pivotally connected at its inner end to the front end of the upper works, by transverse horizontal pin 15. The dipper handle 18 is pivoted at the outer end of boom 17, by transverse horizontal pin 28. The description thus far applies to both Figures 1 and 2.

Turning now to Figure 1, we find that linkage 20 is fastened at one of its ends to boom 17 midway along its span by a brace plate 19. The other end of linkage 24 has a sheave 22 rotatably connected thereto. One end of cable 23 is fastened to the A-frame 16 at a dead-end connection, then passes around sheave 22, then around the A-frame sheave 24, and is spooled onto the excavator winch (not shown).

The hydraulic digging cylinder-piston assembly 21 is pivotally connected at its cylinder end to brace plate 19 and the ram and is pin-connected to the upper end of the dipper-handle 18 by pin 25. Linkage 26 is also pinconnected by pin 25 at one end, and its other end is pinconnected to sheave 22 and to one end of linkage 20 by pin 27.

The dipper-handle 18 rotates about the outer end of boom 17 on pin 28. The dipper 29 is fastened at the lower end of the dipper-handle 18 by a pin 39 and braces 30, so that the dipper may be easily removed from the dipper-handle. Inasmuch as, in the present invention, the handle and dipper operate together, they will be treated g... in the claims to some extent as a single integral instrumentality, sometimes referred to as the handle-dipper assembly.

In Figure 1, tension in cable 23 due to winding-in the cable or to the weight of the boom or both will, if hydraulic fluid is free to flow out of the hydraulic digging cylinder, tend to rotate the dipper-handle 18 counterclockwise and the digging cylinder-piston assembly 21 will retract (piston will move to the left in Figure 1).

If cylinder-piston assembly 21 is locked against re traction and cable 23 is wound-in by the winch, the boom will be raised about its pivotal connection at the front end of the upper works. Similarly, if the assembly is locked against retraction and the winch pays-out cable 23, the boom 17 will be lowered.

When the cylinder-piston assembly 21 is extended by introducing pressure fluid into the assembly, the dipperhandle will rotate clockwise (Figure l) and if the cable 23 is held fixed the boom 17 will be raised slightly.

The combination of the hydraulic digging cylinder-piston assembly and the winch comprises the means for moving the dipperthrough its various cycles.

Figure 2 shows an alternative form of excavator. The two forms of the machine are identical with the following exceptions. In Figure 2, the linkages 20 and 26 are eliminated and sheave 22 is fastened directly to the upper end of the dipper-handle at pin-connection 25. The bydraulic digging cylinder-piston assembly 21 is shifted from the top of the boom to the bottom of the boom, so that it is fastened at one of its ends to brace plate 19 on the bottom of the boom and the other end is fastened to the dipper handle 18 by pin-connection 31 at a point below the dipper-handle pivot-pin 28 and preferably near the lower end of the dipper-handle.

In Figure 2, tension in cable 23 due to winding-in the the cable or to the weight of the boom or both, when the digging cylinder-piston assembly 21 is free to extend, will cause the dipper-handle 18 to rotate counterclockwise. If the cylinder-piston assembly is locked or fully extended winding-in the cable 23 will raise the boom.

In Figure 1, the digging force is applied when the hy' draulic digging cylinder-piston assembly 21 extends whereas in Figure 2, the digging force is applied when the hydraulic digging cylinder-piston assembly 21 contracts.

Now turning to Figures 3 and 4, we find the details of dipper 29 and dirt-ejector 32.

Dipper 29 has a movable Wall 32 (hereinafter called the dirt-ejector), pivoted about hinge 33 at its open upper end. This'diIt-ejector' when-swung about hinge 33 (from position A to position B in Figure 3) will sweep through the cavity of tbedipper and clean out the contents. The ejector may then be swungback to the retracted or fulldipper position (position A in Figure 3). The ejector is moved about its axis (on hinge 33) by the double-acting ejector cylinder-piston assembly 34. One end of the hydraulic ejector cylinder-piston assembly 34 is connected by pin 36 to a bracket 35 which is part of the dipperhandle 18. The other end of cylinder-piston assembly 34 is connected by pin 38 tobracket 37 which is part of the back face of the dirt-ejector 32.

The hydraulic diagram shown by Figure corresponds tothe showing of Figure 1. From Figure 5, wefind that 48 is the main fluid tank and pump 47a is the main source of pressure for the excavator hydraulic system. A fluid conduit extends from the main tank to the inlet of pump 47a to furnish fluid to the pump. 40 is a three-position hydraulic selector valve as shown. By three-position valve is meant that the valve has three setting positions, namely: 1) a power-on position whereby pressurefluid flows through the valve and into the cylinder-piston assembly, thereby furnishing it with power; (2) a hold position which prevents fluid from either entering or leaving the cylinder; and (3) exhaust. position, whereby fluid will flow from the cylinder back into the main reservoir. A fluid conduit 45 extends from the main pump to selector valve 40. Selector valve 40 is connected to port 44a on the hydraulic digging cylinder-piston assembly 21 and to port 46 on ejector cylinder-piston assembly 34 by fluid conduits 51 and 50, conduit 50 being T-connected to conduit 51 at some convenient point 49 intermediate its ends. An exhaust conduit 54 extends from valve 40 to the main tank 48.

A fluid conduit extends from the main tank to an auxiliary source of hydraulic fluid pressure, pump 47b, which furnishes power to move the dirt-ejector to dump the dipper. An alternative arrangement could easily be contrived, whereby pump 47a could furnish pressure for the purposes stated herein as served by pumps 47a and 47b. A fluid conduit 61 extends from the auxiliary pump 4712 to a second selector valve 56. Selector valve 56 is a twoposition hydraulic-selector valve as shown. By two-position valve is meant that the valve has two setting positions, namely: (1) a power-on position whereby pressure fluid flows through the valve and into the cylinder-piston assembly, thereby furnishing it with power, and (2) an exhaust position, whereby fluid will flow from the cylinder back into the main reservoir. Selector valve 56 is connected to port 60 on the hydraulioejector cylinderpiston assembly 34 by fluid conduit 59. An exhaust conduit 62 extends from selector valve 56 to main tank 48.

When it is desired to dig, selector valve 56 is set to the exhaust setting which connects port 58 with port 55, and selector valve 40 is set to the power-on setting, which connects port 42 with port 41, said settings being made in that order. Pump 47a supplies pressure fluid through conduit 45 into port 42, then into port 41, and through conduit 51. Conduit 50 connects to port 46 on the cylinder of ejector cylinder-piston assembly 34 and conduit 51 connects to port 44a on the cylinder of digging cylinder-piston assembly 21. If the dirt-ejector 32 is not in the fully-retracted position, the pressure-fluid will first cause the ram of cylinder-piston assembly 34 to move to the fully-retracted position, due t'o'the fact that the piston of this cylinder will normally offer less resistance in this position than the piston of the digging cylinder-piston assembly 21. As pressure fluid enters port 45, cylinderpiston assembly 34 retracts. Fluid is exhausted through port 60 of cylinder-piston assembly 34, through conduit 59, into selector valve 56 at port 58. Thus, exhaust fluid flows from port 58 into port 55, through conduit 62 into main fluid tank 48. After the ejector ram has been fully retracted (position A in Figure 3), pressure-fluid from the pump will flow only through conduit 51 and into port 44a, thus moving the piston of the digging cylinder-piston assembly 21 causing the assembly to extend and rotate the dipper-handle clockwise (Figure 1). By this arrangement, whenever selector valves 48 and 56 are thus set. hydraulic power will be furnished to the hydraulic digging cylinder-piston assembly 21 to dig, and the dirt cjector 32 will always be first returned to the fully-retracted or digging position (position A in Figure 3) before pressure fluid is supplied to the cylinder of the digging cylinderpiston assembly 21 for digging.

Return of the ejector and dumping of the dipper are produced with the above-described hydraulic circuits by the action of gravity. When selector-valve 46 is in the hold position so that fluid-port 52 is blocked off, the weight of the boom will tend to retract cylinder-piston assembly 21 (Figure 1) thereby setting up fluid pressure in circuits 51 and 50. Then if selector valve 56 is in the exhaust position, pressure fluid will flow from conduit 51 through connection 49, through conduit 50. and

through port 46 of cylinder 34 causingsaid cylinder to retract and thereby return the ejector. Return fluid from cylinder 34 flows from port- 60 through conduit 59 through ports 58 and 55 through conduit 62 into tank 48. When selector valve 40 is set in the exhaust position so that fluid from piston 21 will flow through conduit 51 through ports 41 and 52 through conduits 54 into tank 48, the

weight of the boom will retract cylinder-piston assembly 21, and the handle-dipper assembly will rotate anticlockwise about pivot pin 28. Thus it can be seen that by making use of the potential energy of the boom in its raised position, dumping of the dipper and return of the ejector are accomplished. This has the advantage that both digging and dumping are produced with one singleacting hydraulic cylinder having one hydraulic pressurefluid connection, and ejection and return of the ejector are also both produced by a single hydraulic cylinder.

After the dipper has taken a cut of earth, the boom is raised under power of the winch and the upper work is swung on pintle 14 by conventional means to a dumping position. One method of raising the boom is to set the selector valve 40 in the hold position. This will lock the fluid in cylinder-piston assembly 21 and prevent the dipper handle from rotating. The winch is then actuated to haul-in on cable 23, thus raising the boom. Also, the boom may be raised while cylinder-piston assembly 21 is being extended. This is done by winding-in cable 23 on the winch.

Tension in cable 23 due to the weight of the boom will cause the handle-dipper assembly (Figure 1) to rotate anticlockwise into a dumping position when selector valve 40 is set to connect port 41 to port 52, so that the fluid in the digging ram cylinder may exhaust back through selector valve 40, through conduit 54 into main fluid tank 48 to allow the digging cylinder-piston assembly 21 to retract, i. e., piston moves to the left in Figure 5.

When it is desired to dump dirt from the dipper 29 by use of the ejector 32, selector valve 56 is then set to the power-on setting 30 that port 57 is connected with port 58. This causes pressure-fluid from pump 47]) to flow through conduit 61 into port 57, to port 58, and through conduit 59 into port 60 of the double-acting ejector cylinder-piston assembly 34, and thus cause the ram to extend downward and pivot dirt-ejector 32 about its axis (at hinge 33) to the dipper-emptying position (position B in Figure 3); which will dump and clean the dipper cavity. The fluid on the exhaust side (lower side in Figure of the cylinder of ejector cylinder-piston assembly 34 will flow out through port 46, then through conduit 50, through joint 49 into conduit 51.

If the piston of digging cylinder-piston assembly 21 is not fully extended the selector valve 40 will generally be set to the hold position. This will control the dipperhandle, whereby the position of the handle in relation to the boom will remain unchanged after valve 40 is set in the hold position. The exhaust fluid from assembly 34 will exhaust through conduit 51, through port 44a, and into cylinder-piston assembly 21. This will cause the ram of assembly 21 to extend slightly; since the area of the rod end of the piston of ejector cylinder-piston assembly 34 is small in comparison to the area of the piston of assembly 21, such extension will not be objectionable as it is very small. If it is desirable to release the dipper-handle so that it will be free to rotate about its pin 28 on the boom, then the selector valve 44) may be set to the exhaust setting by connecting port 41 to port 52. and thus exhaust fluid from the cylinder of ejector cylinder-piston assembly 34 and exhaust fluid from the cylinder of the digging cylinder-piston assembly 21 will flow from port 41 into port 52 on valve 40, through conduit 54, and into the main fluid tank 43.

The combined eflect of the two alternative settings of selector valve 46) (described above), i. e., (a) set in the hold position, -or (b) set in the exhaust position, may be achieved through cracking valve 40. By cracking valve 40 is meant to set it to the hold position, then momentarily set it in the exhaust position, and then move it back to the hold position. By doing this the dipper-handle position can be maintained in a relativelyfixed position, and through cracking valve it), a certain amount of exhaust fluid in conduit 51 will be allowed to flow back to the main tank. This method of control is.

Lin

6 desirable when the ram of cylinder-piston assembly 21 fully extended or almost fully extended.

The hydraulic diagram shown in Figure 6 corresponds to the second embodiment of this invention as shown by Figure 2. The diagram of this Figure 6 is the same as Figure 5 except as follows. Port 44b is located at the opposite end of the cylinder of digging cylinder-piston assembly 21, ascornpared to port 44a of Figure 5, so that when pressure fluid flows through conduit 51 from pump 47a, the digging cylinder-piston assembly will retract (piston will move towards the upper Works in Figure 2) instead of expand (piston moving away from the upper works in Figure 1). The flow of fluid and the control valve settings are the same for both Figures 5 and 6.

Having now described and illustrated two forms of this invention, let it be understood that this invention is not to be limited to the specific form or arrangement of parts hereinbefore described, except insofar as such limitations are specified in the appendant claims.

The number of positions recited in the claims for any valve, is to be considered as the necessary and sufiicient number of positions, and to include valves having a greater number of positions for any additional functions which may be desired.

The best mode contemplated by the inventor for carrying out the invention is that shown in Figures 1, 3, 4, and 5.

We claim:

1. In an hydraulically-operated excavator, having: a main frame; a boom having its foot pivotally supported by the main frame; a handle-dipper assembly, comprising a handle and a digging-dipper secured to the lower end of the handle; a pivotal connection between the outer end of the boom and the handle; first power means, connected to a portion, remote from said pivotal connection, of the handle-dipper assembly and to the main frame, for raising and supporting the boom; and second power means, hydraulic-ally connecting the handle-dipper assembly to the boom, for swinging the assembly about its pivotal connection on the boom in a direction to cause the dipper to dig; the combination therewith of: an ejector, associated with the digging-dipper; means shiftably connecting the ejector to the handle-dipper assembly; third power means reversible hydraulic, for shifting the ejector alternatively to eject dirt and to retract the ejector; hydraulic fluid pressure source means; hydraulic circuit means connecting the pressure-source means to the two hydraulic power means; control means, interposed in said circuit means to provide or block at will communication between said pressure-source means and said two hydraulic power means; and fluid conduit means interconnecting said two hydraulic power means to produce interaction therebetween in at least one power function of said two hydraulic power means and to actuate the third power means by hydraulic fluid under pressure of the weight of the boom displaced by the second power means.

2. In an hydraulically-operated backhoe excavator, having: a main frame; a boom having its foot pivotally supported by the main frame; a handle-dipper assembly, comprising a handle and a digging-dipper secured to the lower end of the handle; a pivotal connection between the outer end of the boom and the handle; first power means, connecting the handle-dipper assembly to the main frame, for raising the boom; and second power means, hydraulic, connecting the boom and the handle-dipper assembly, for swinging the assembly about its pivotal connection on the boom; the combination therewith of: an ejector, associated with the digging-dipper; means pivotally connecting the ejector to the handle-dipper assembly; third power means reversible hydraulic, connecting the ejector to the handle-dipper assembly, for pivoting the ejector alternatively to eject dirt and to retract the ejector; hydraulic fluid pressure means; hydraulic circuit means connecting the pressure means to the two hydraulic power means to actuate said hydraulic power means; conduit means interconnecting the second and third power means, the relative forces of .the second and third power means, and the normal relative loads to be moved by each, being such that when the third power means is actuated to retract the ejector, the third power means is normally operated before the second .power means; and control means, including a selector valve, for controlling the flow of fluid to each hydraulic power means and to the interconnecting conduit means, interposed in the hydraulic circuit means, for at will either (1) sequentially actuating the third power means to retract the ejector and then actuating the second power means to cause thedipper to approach the main frame, or (2) permitting the second power means to permit the dipper to be swung away from the main frame and permitting the third power means to move the ejector to eject dirt, or (3) preventing both foregoing alternatives and at will either (a) actuating the third power means to move the ejector to eject dirt, or (b) permitting the third power means to retract the ejector.

3. An hydraulically-operated backhoe excavator according to claim 2, further characterized by the fact that the second power means comprises: a single-acting hydraulic cylinder-piston assembly, expandable under hydraulic pressure; means pivotally connecting one end of said hydraulic cylinder-piston assembly to the boom at a point intermediate the ends of the boom; means connecting the other end of said hydraulic cylinder-piston assembly to a pivotal connection adjacent the upper end of the handle; whereby the expansion of said hydraulic cylinderpiston assembly under hydraulic pressure can swing the handle about its pivotal connection on the boom in a direction to cause the dipper to approach the main frame.

4. An hydraulically-operated backhoe excavator according to claim 2, further characterized by the fact that the second power means comprises: a single-acting hydraulic cylinder-piston assembly, contractable under hydraulic pressure; means pivotally connecting one end of said hydraulic cylinder-piston assembly to the boom at a point intermediate the ends of the boom; means connecting the other end of said hydraulic cylinder-piston assembly to a pivotal connection on the handle-dipper assembly at a point intermediate the pivotal connection of the handle to the boom and the lower end of the handledipper assembly, whereby the retraction of said hydraulic cylinder-piston assembly under hydraulic pressure can swing the handle about its pivotal connection on the boom in a direction to cause the dipper to approach the main frame.

5. An hydraulically-operated backhoe excavator according to claim 2, further characterized by the fact that the second power means is an hydraulic cylinder-piston assembly, that its points of connection to the boom and to the handle-dipper assembly are both remote from the pivotal connection of the handle on the boom; and that I the control means, hydraulic pressure means and the hydraulic circuit means comprise: a main tank; a fluid-pressure source; fluid conduit means extending from the main tank to the pressure source; a three-position selectorvalve; fluid conduit means extending from the pressure source to said selector-valve; fluid conduit means extending from the selector-valve to the main tank; a port on the hydraulic cylinder of the second power means, for the admission of fluid to actuate said:power means; a first port on the hydraulic cylinder of the third power means, for the admission of fluid to actuate said'power means to retract the ejector; fluid conduit means interconnecting the selector-valve, the port on the second power means, and the first port on the third power means for common control of said second and third power means; and selective means to at will actuate said third power means to cause the ejector to eject dirt.

6. In an hydraulically-operated backhoe excavator having a main frame, a boom pivotally mounted on the main frame, ahandle-dipper assembly pivotally connected to the' outer end of the boom; a dipper connected to the lower end of the handle-dipper assembly; an ejector shiftably connected to said handle-dipper assembly; the combination of: first power means connecting the main frame to the boom, for raising and lowering the boom; second power means, hydraulic, connecting the handledipper assembly to the boom to rotate said assembly about its pivotal connection on the outer end of the boom; third power means, reversible hydraulic, pivotally connected to the handle-dipper assembly and to the ejector for shifting the ejector with respect to the handle-dipper assembly, alternatively to clean the dipper or to retract the ejector; the relative forces of the second and third power means, and the normal relative loads to be moved by each, being such that when the third power means is actuated to retract the ejector, the third power means is normally operated before the second power means; and means interconnecting said second and third power means for common actuation of said second power means sequentially to rotate said assembly and of said third power means to retract the ejector.

7. In an hydraulically-operated backhoe excavator the combination of: a main frame, a boom pivotally supported by the main frame, a handle-dipper assembly pivotally connected to the boom for fore-and-aft jackknife swinging motion with relation thereto; a dipper suspended at the lower end of the handle-dipper assembly; an ejector shiftably connected to the handle-dipper assembly; first power means connected to the main frame and to the boom to raise and lower and support the boom, said first power means including a first cylinder-piston assembly; a second hydraulic cylinder-piston assembly, connecting the handle-dipper assembly to the ejector for shifting the ejector alternatively to eject dirt or to retract the ejector; hydraulic fluid-pressure source means; hydraulic circuit means connecting the fluid-pressure source means to the two cylinder-piston assemblies; control means interposed in the fluid-circuit means to provide or block at will communication between said source means and said first cylinder-piston assembly; fluid connections independent of said control means interconnecting said first and second cylinder-piston assemblies whereby, when the control means blocks communication from said source means to the first cylinder-piston assembly the second cylinderpiston assembly will be actuated by fluid under pressure of the weight of the boom displaced by and passing from the first cylinder-piston assembly to the second cylinderpiston assembly.

8. An hydraulically-operated backhoe excavator according to claim 7, further characterized by the fact that the first hydraulic cylinder-piston assembly is connected to the handle-dipper assembly and to the boom to swing the handle-dipper assembly about its pivotal connection on the boom. 4

References Cited in the file of this patent UNITED STATES PATENTS D. 162,873 Pilch Apr. 10, 1951 2,418,299 Gorsuch Apr. 1, 1947 2,613,822 Stanley Oct. 14, 1952 2,638,237 'Struthers et al. May 12, 1953 2,742,165 Pilch Apr. 17, 1956 

